1. Field of the Invention
This invention relates to a magnetic tape cassette, and more particularly to a magnetic tape cassette comprising a cassette body having high shock fracture strength.
2. Description of the Prior Art
A magnetic tape cassette comprises a pair of reel hubs around which a magnetic tape is wound retained in a cassette body. In general, the cassette body is fabricated of a plastic material or the like by injection molding and the manufacture and the mass production thereof are easy. The cassette bodies manufactured according to the conventional methods, however, have a drawback of possessing relatively low shock fracture strength owing to the properties of plastic materials and are prone to damage when, for example, the cassettes happen to drop to the floor. Especially when a material of the polystyrene series or the like is used for improving the heat resistance of the cassette body to equip it for outdoor use, the shock fracture strength thereof is low and the cassette body is likely to be damaged by the aforesaid accidental drop. Further, the cassettes manufactured according to the conventional methods have another drawback that the surfaces thereof are likely to become dusty, since plastic material has high electric resistance and, therefore is likely to become electrically charged.
In view of the drawbacks, the present applicant proposed a cassette body wherein a protective film layer is formed on the surface of the cassette body by disposing a film of polyethylene or the like in a cavity of an injection mold at the time injection molding is to be conducted and unitedly connecting the film to the surface of the cassette body simultaneously with the injection molding. Since the cassette body thus manufactured is provided with a protective film layer, the cassette body has an improved shock fracture strength, but is still disadvantageous in that it is difficult to form the protective layer over the entire outer surface of the cassette body for reasons relating to the formability of polyethylene film or the like. In addition, polyethylene or the like is also likely to be electrically charged and, it is therefore necessary to provide an antistatic layer on the surface of the polyethylene film or the like.